1. Technical Field of the Invention
The present invention relates to a process for producing 3,9-bis(2-chloroethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (hereinafter, sometimes abbreviated as Compound (I)) useful as a synthetic intermediate. 
2. Related Art
Compound (I) is a useful intermediate raw material for synthesizing various bifunctional derivatives having a spiro acetal skeleton. As a known production method thereof, there is known a method comprising two steps, i.e., firstly, (1) the synthesis of 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane (hereinafter, abbreviated as Compound (II)) by reacting acrolein with pentaerythritol in the presence of p-toluenesulfonic acid, and successively, (2) the synthesis of Compound (I) by reacting Compound (II) with hydrogen chloride (Spanish Patent No. 324610 (1966)). According to Examples thereof, the yields in the reactions (1) and (2) are relatively high, i.e., 81.5% and 81%, respectively, but the method requires many operations owing to the fact that the method involves a two-step reaction, so that it is not necessarily efficient.
On the other hand, the synthesis of 1,1-dialkoxy-3-chloropropane by reacting acrolein, an alcohol such as methanol ethanol or the like, and hydrogen chloride has been hitherto known (Org. Syn. Coll. vol. 2, 137 (1943)). According to the literature, 1,1-diethoxy-3-chloropropane (hereinafter, abbreviated as Compound (III)) is synthesized by adding acrolein into ethanol saturated with dry hydrogen chloride gas, whereby the acrolein, the hydrogen chloride and the ethanol are reacted with each other. However, the yield is only 34% because various by-products are formed.
As an attempt to improve the yield by suppressing the formation of the by-products in the above reaction, there is a report that Compound (III) was obtained in 87.7 to 91% yields by adding an anhydrous ether solution of acrolein into anhydrous ether in which dry hydrogen chloride had been absorbed, followed by adding absolute ethanol and molecular sieves thereto (Proc. Jpn. Acad., Ser. B, 56(9), 573 (1980)). One of the points of this method lies in the exhaustive exclusion of water from the reaction system. Therefore, the method is not economical in the industrial use, because the raw materials should be made anhydrous and molecular sieves are used in a large amount.
In consideration of the above situation, it is an object of the present invention to provide a process for obtaining Compound (I) conveniently in high yields.
As a result of the extensive studies for achieving the above object, the present inventors have found that Compound (I) can be obtained conveniently in high yields by reacting acrolein, pentaerythritol, and hydrogen chloride at one step. Based on such findings, they have accomplished the present invention.
Accordingly, the present invention relates to a process for producing 3,9-bis(2-chloroethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane comprising a step of reacting acrolein, pentaerythritol, and hydrogen chloride at one step.
In the following will be described the present invention in detail.
According to the present invention, acrolein is used in an amount of 1.6 to 3.0 moles, more preferably 2.0 to 2.5 moles, per 1 mole of pentaerythritol. The use of an excess of acrolein is not preferable because unreacted acrolein and 3-chloropropanal may remain in the reaction system.
In the reaction of the present invention, hydrogen chloride acts as the reaction catalyst as well as a reactant. Equimolar or more amounts of hydrogen chloride are required per 1 mole of acrolein to be used. Hydrogen chloride is used in the reaction after the dry gas thereof has been absorbed in a solvent. Alternatively, in the reaction of the present invention, hydrochloric acid can be also used instead of hydrogen chloride gas, in other words, the hydrogen chloride can be in the form of hydrochloric acid. In the aspects of the handleability and the economical efficiency, the use of hydrochloric acid is industrially more advantageous.
Since the aimed-at Compound (I) is a solid substance at ordinary temperature and is sparingly soluble in water, it is preferable to add to the reaction system, an inert solvent in which Compound (I) is soluble not only in the case of using hydrogen chloride gas but also in the case of using hydrochloric acid. The solvents usable include aromatic solvents such as toluene, xylene, tetramethylbenzene, and the like; aliphatic and alicyclic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, petroleum ether, cyclopentane, cyclohexane, and the like; ethers such as diethyl ether, THF, and the like; acetonitrile; and the like. For the purpose of facilitating the post-treatment after the reaction, a solvent having a low solubility in water is suitable.
As other additives, in order to prevent the polymerization of acrolein, a polymerization inhibitor such as a multivalent phenol, e.g., hydroquinone, p-t-butylcatechol, or the like may be added in a slight amount.
The following will explain the reaction itself and subsequent post-treatment step after the reaction.
To pentaerythritol is added hydrochloric acid (and a solvent) or a solvent in which dry hydrogen gas has been absorbed. With stirring the resultant mixture, acrolein is added gradually thereto. Acrolein may be added after it has been mixed with a solvent and/or a polymerization inhibitor beforehand. Alternatively, the polymerization inhibitor may be added to la mixture of pentaerythritol and hydrogen chloride. The reaction proceeds as acrolein is added. The reaction mixture is kept at a temperature of xe2x88x9220xc2x0 C. to 60xc2x0 C., preferably 0 to 40xc2x0 C.
After the completion of the reaction, hydrogen chloride present in excess is neutralized with an alkali (aqueous solution) of sodium hydrogen carbonate, sodium carbonate, sodium hydroxide, or the like. In that case, an organic layer containing the aimed-at Compound (I) can be easily separated, by using a solvent having a low solubility in water.
Since Compound (I) is used as an intermediate for synthesis, the purification is carried out according to the purity required in the subsequent synthetic reaction in which the compound is used as a raw material. In the simplest case, the above solution after the neutralization is provided as it is to the next reaction. On the other hand, in the case where a high purity is required, after the removal of the solvent by evaporation, the compound is isolated/purified, for example, by further distillation under reduced pressure or by recrystallization from an acetone-water mixed solvent, a methanol-water mixed solvent, or the like.
In the synthesis of 1,1-dialkoxy-3-chloropropane by reacting acrolein, an alcohol, and hydrogen chloride, it is common to use dry hydrogen chloride gas, because the reaction for acetalization is an equilibrium reaction involving the formation of water. In the process of the present invention, the aimed-at compound can be obtained in high yields even when hydrochloric acid is used. The reason may be presumed from the dissolving properties of the raw materials and the aimed-at Compound (I) as follows. That is, pentaerythritol is a crystalline substance having a high melting point (260xc2x0 C.) and has characteristics that it is soluble in water, ethanol, glycerol, or the like but is insoluble in most of organic solvents. On the other hand, the aimed-at Compound (I) has a low solubility in water. Therefore, the reaction occurs or proceeds in hydrochloric acid, but the equilibrium is shifted by the precipitation of the aimed-at Compound (I) formed from the hydrochloric acid, so that it is considered that the aimed-at compound can be obtained in high yields.